The present disclosure relates generally to adsorptive members and/or adsorptive filters, and more particularly to filters useful for adsorbing hydrocarbon vapors.
In internal combustion engines, while the engine is running, there is a constant flow of air through the air induction system into the intake manifold and finally into the combustion chamber through the intake valves. The airflow is caused by the intake stroke of the piston, which draws a vacuum on the intake manifold. This creates an imbalance of pressures between the intake manifold and the environment, and thus air rushes in through the air induction system. Due to the low internal pressure in the intake manifold and the constant airflow into the engine during engine operation, there are no evaporative emissions out through the inlet opening of the intake manifold or air induction system.
In addition, and when a fuel injected engine is running, a fuel system maintains the fuel in the fuel rail(s) at sufficient pressure to prevent the vaporization of the fuel even though the fuel rail(s) may be at a temperature sufficient to vaporize the fuel at normal atmospheric pressure. In fact, good restarting in part may depend on maintaining fuel rail pressure for a number of hours after shut down until the engine cools to prevent fuel vaporization in the fuel rail(s). Fuel vapor in the fuel rail(s) is generally undesirable in that it may lead to long crank times during engine start up.
After engine shut-down, air continues to rush through the air induction system until the intake manifold vacuum is eliminated. Evaporative hydrocarbons may be emitted if the pressurized fuel in the fuel rail(s) leaks into the intake manifold through the fuel injectors or un-combusted fuel in the system is present. This small amount of fuel may vaporize, and the hydrocarbon vapor may migrate out of the intake manifold through the inlet opening of the air induction system into the atmosphere. In the past, such hydrocarbon vapor egress was considered negligible. However, current regulations and environmental awareness have created the need to provide internal combustion engines wherein evaporative emissions from the air induction system are virtually zero.
Attempts to solve the problem of evaporative hydrocarbon emissions have included placing secondary, hydrocarbon adsorbing filters directly or across the direct air flow path. However, by disposing an extra layer of filtration media across this flow path causes an additional flow restriction to be placed upon the air induction system. As such, the engine is generally less efficient, or the air induction system may need to be sized larger in order to provide the same mass airflow with the increased restriction.
Other attempts have included combining hydrocarbon vapor-adsorbing materials with a standard particulate/contaminant air filter. Some drawbacks associated with these combination filters include the possibility of vapor-adsorbing material flaking out of the filter and entering the air system. The loss of adsorbent material may deleteriously affect the vapor absorbance of the filter.
Accordingly, it is desirable to provide a filter, apparatus and method of manufacture wherein the hydrocarbon absorber is capable of providing the desired hydrocarbon emission reduction without adversely affecting the performance of the air induction system.